The present invention relates to the field of medical dialysis. More particularly, it relates to an improvement in grafts designed to reduce the frequency of graft failure. Although the invention can be adapted to a wide range of uses, it is especially well-suited for use in the dialysis field. Other uses could be, but are not limited to, intravenous hyperalimentation, frequent prolonged venous access as with chemotherapy, plasmapheresis, leukopheresis, repetitive venipuncture, etc.
Currently in excess of 200,000 patients undergo dialysis therapy, 85 percent of whom undergo hemodialysis. This process involves removing toxic waste products from the blood by convection and diffusion through a semipermeable membrane known as an artificial kidney. Dialysis has been available for patients with kidney failure for over 30 years. Widespread use of the process began in the United States in 1972 with the passage of the End-Stage Renal Disease Program under Medicare legislation. The treatment of chronic kidney failure requires this dialysis process to remove the toxic chemicals which accumulate in the blood as a result of normal metabolic processes of the body. This is done by exposing the waste filled blood to a clean dialysis solution via a semipermeable membrane in the artificial kidney. This process permits uni-directional osmotic difflusion of the noxious waste substances to flow from the blood side of the membrane to the dialysate side after which the waste filled dialysate is disposed. To enable adequate volumes of blood to be exposed to the dialysis membrane the patient's veins must be enlarged by creating conduits between arteries and veins. These artificial conduits, called grafts, allow a high rate of blood to flow through them and when connected with dialysis needles deliver large volumes of blood to the dialysis membrane through the dialysis machine.
This process occurs three times per week, or thirteen times a month and lasts for approximately three to four hours per session. The grafts are usually constructed of a synthetic material such as Dacron, Gortex, polyurethane, PTFE, silicone, or other materials known in the art. The life expectancy of these grafts varies from six months to two years and is limited by stenosis, infection, and clotting. Regardless of the graft material used, all current graft designs include a cylindrical tube fashioned to fit a circular, elliptical, or marquis-shaped anastomosis from an artery to a vein. Straight, curved, or U-shaped grafts are available for a variety of connections, depending upon the position of the desired graft. Nevertheless, the working portion of all grafts are cylindrical tubes with a variety of shapes and a variety of fixed luminal diameters throughout the graft's length.
Regardless of the graft design, two major types of problems often occur. The first is difficulty with cannulation to access the graft and the second is bleeding from the graft site. The first problem is that the graft is too narrow or too deep to cannulate and the dialysis staff cannot accurately place the needles into the graft to achieve adequate blood flow. This problem is typically caused by; the luminal diameter being too small in cross-section or the graft being too deep to appreciate its anatomical location within the patient. Inaccurate needle placement is the usual result.
The second problem, that of leakage of blood from either a hole or laceration of the graft, is a result of erroneous needle cannulation. A common problem encountered with graft bleeding is hemorrhage below the graft, so called infragraft hemorrhage, which occurs when the needle is placed too far into the graft resulting in backwall perforation. This occurs in an estimated 25-30 percent of all cannulations. This type of perforation is not immediately obvious to the naked eye and can cause sufficient hemorrhage around the graft to occlude the graft from extreme pressure caused by the hemorrhage. This usually leads to complete loss of the graft.